This invention relates to methods of sintering nanophase materials and more particularly to sintering nanocrystalline ceramics in order to increase densities while retaining small grain size. Ceramics find many uses in industry particularly for electrical components. However, internal flaws and high temperature processing along with negligible ductility of ceramics are problems which mitigate against their uses. Improved physical characteristics have been achieved by reducing the particle size of the starting powders from which the ultimate ceramics are made. Small particle sizes have the advantages that densification depends inversely on the fourth power of particle size, internal flaws associated with larger pores are minimized, and ductility can be gained through other mechanisms known in the art. Ultra fine grain metals have been prepared by Glaiter about 10 years ago, Deformation of Polycrystals: Mechanisms and Microstructures, N. Hansen et al. eds (Ris National Laboratory, Roslalde, Norway 1981), in which inert gas condensation of metal vapors is combined with in situ collection and compaction of the ceramic powders to produce nanocrystalline ceramics. These ceramics have potentially important properties such as low sintering temperatures and superplasticity. By nanocrystalline materials, it is meant in this application, materials having average grain sizes of 100 nanometers or less and preferably grain sizes of 60 nanometers or less. Green body density of ceramic nanocrystalline materials can approach 75% of theoretical, but for most purposes densities of the fired ceramic should be greater than about 90% of theoretical.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.